How to Calculate Gas Law
What is Gas Law?
Gas law calculators solve Boyle's, Charles's, Gay-Lussac's, and the combined gas law for pressure, volume, and temperature relationships of ideal gases.
Formula
PV = nRT (ideal gas law); P₁V₁/T₁ = P₂V₂/T₂ (combined gas law)
- P
- Pressure (atm/Pa)
- V
- Volume (litres/m³)
- n
- Moles of gas (mol)
- R
- Gas constant (0.0821 L·atm/(mol·K))
- T
- Temperature (Kelvin)
Step-by-Step Guide
- 1Boyle's law: P₁V₁ = P₂V₂ (constant T)
- 2Charles's law: V₁/T₁ = V₂/T₂ (constant P)
- 3Gay-Lussac's: P₁/T₁ = P₂/T₂ (constant V)
- 4Combined: P₁V₁/T₁ = P₂V₂/T₂
Worked Examples
Input
Boyle's: V₁=4L, P₁=2atm, P₂=4atm
Result
V₂ = P₁V₁/P₂ = 2×4/4 = 2L
Frequently Asked Questions
When should I use ideal gas law vs combined?
Ideal: when n (moles) is constant or unknown. Combined: when gas amount is fixed, conditions change.
What temperature units should I use?
Always Kelvin (K = °C + 273.15) in gas law equations. Celsius and Fahrenheit don't work.
Is the ideal gas approximation accurate?
Good for most gases at normal conditions. Poor at high pressure or low temperature. Use van der Waals for precision.